Nuke Silo = Ancient Monument???

So my mate T calls on Saturday and in the conversation mentions he passed by Greenham Common that day. Now for those of you who don't know it RAF Greenham Common is, as the name implies, common land, for use by the people, but commandeered by the RAF for time as an airstrip. It was used in WWII by the US 101st Airborne for glider ops in Normandy 1944, later for the US Strategic Air Command in the '50s for carrying nuclear payloads and later again, from 1980 onwards, for the deployment of cruise missiles, aka NUKES!

Back in the '80s the place was renowned for its women's peace camp and at one stage as many as 300,000 people linked hands around the base in protest against the nuclear missiles being there! Hundreds of people were arrested, as you can imagine. You could also score good weed there, or so I'm told.

So, I went and had a butchers at the place, it's only 30 minutes away, and in the last 6/7 years it has been decomissioned and turned back into natural heathland where nature flourishes, animals once again graze and people come and go; flying kites, walking, biking, watching birds, letting their dogs crap and their kids cycle there. Though that last combination worries me now I've written it :S The peace camp left when the nukes did, so all's well that ends well :)

And I started with Nuke Silo = Ancient Monument??? Yes I did. And here's why I ask the question... These nuclear silos are only 50 years old and yet the site is designated as an "Ancient Monument"!!???